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Question
Sat February 16, 2013 By:

# 1.Why a mirror has one principal focus while a lens has two principal foci? 2.Calculate the distance at which an object should be placed in front of convex lens of focal length 10cm to obtain an image double its size?

Mon February 18, 2013
Please post aone query at a time.
The reason why a lens has two focii while a mirror has only one is because of the fact that light is transmitted through a lens and not a mirror. Unlike in mirrors, images in lenses can form on either side and thus we require two focii to properly determine the formation and position of an image.
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